1. Field of the Invention
The present invention relates to line drivers used in communication systems, such as in digital subscriber line (DSL) systems.
2. Background Art
DSL (digital subscriber line) technology provides for the digital transmission of data over the wires of a local telephone network. Typically, in a DSL system, an Internet service provider (ISP) interfaces with an analog telephone line using a DSL modem. The DSL modem enables the ISP to communicate with consumers over the analog telephone line. A consumer also interfaces with the analog telephone line using a DSL modem to perform communications with the ISP. The DSL modem of the consumer extracts digital data from the analog telephone line that was transmitted by the ISP, and provides the extracted digital data to a computer of the consumer. Furthermore, the DSL modem of the consumer transmits digital data that was received from the computer to the ISP over the analog telephone line. Typically, the download speed of consumer DSL services ranges from 512 kilobits per second (kbit/sec) to 24,000 kbit/sec, depending on the type of DSL technology.
Various types of DSL technology exist, including Asymmetric Digital Subscriber Line (ADSL) and VHDSL or VDSL (Very High Speed DSL). In ADSL, upstream communication speeds (e.g., for transmissions from the consumer) are lower than downstream communication speeds (e.g., for transmissions from the ISP). With standard ADSL, a frequency band of 25.875 kHz to 138 kHz is used for upstream communications, and a frequency band of 138 kHz-2.2 MHz is used for downstream communications.
VDSL is a newer standard that provides for faster data transmissions than standard DSL or ADSL. For example, VDSL is capable of supporting new high bandwidth applications such as HDTV. Communications according to VDSL are symmetric such that upstream and downstream communications may be performed at the same rates. Second-generation VDSL (VDSL2) systems utilize a bandwidth of up to 30 MHz to provide data rates exceeding 100 Mbit/s in both the upstream and downstream directions. The maximum available bit rate may be achieved at relatively short ranges, such as a range of up to about 300 meters.
As the different types of DSL technologies become more widespread, DSL modems with multi-DSL technology capability are becoming desired. For example, DSL modems that support both the VDSL standard along with the more prevalent ADSL standard are desired. However, to save costs, it is desired for DSL system solutions to use fewer components to reduce the resulting bill of materials (BOM). Such cost pressures are making it more difficult to implement DSL modems with multi-DSL technology capability.
Thus, ways of enabling multi-DSL technology capability in DSL modems, without substantially increasing costs, are desired.